In the operation of internal combustion engines, it is known that to form a stratified charge within the engine cylinders offers a number of operating advantages. Primarily, the provision of a stratified charge condition within the engine permits the use of a wider variety of fuels than is normally found with a premixed, carbureted charge. Further, by the proper regulation of the fuel flow, and its subsequent combustion, the combustion process can be completed quickly and efficiently thereby obtaining maximum power from the amount of fuel utilized.
It has also been determined that through the proper regulation of fuel and air introduction to the engine cylinders, the resulting quality of air polluting elements contained in the engine exhaust gas can be regulated. These air polluting elements such as NO.sub.x and CO can be minimized to a point where they are in compliance with strict standards which are set, and which are considered to be safe for automotive operation.
Toward facilitating the combustion process in an internal combustion engine, the use of a cavity or depression formed into the face of a piston is known. Such a cavity serves the function of not only providing an initial combustion chamber, but also, as in the present instance, increases the swirl rate of air which is introduced prior to forming the combustible charge.
As taught in U.S. Pat. No. 3,094,974, the controlled production of a swirling air stream, when coordinated with the rate of introduction of fuel, results in a highly efficient internal combustion engine operation. In said engine a predetermined quantity of fuel is injected into the combustion chamber, and an air stream is introduced through the engine intake port by means of a shrouded valve or similar means such that the entering air stream forms a rapidly rotating mass guided by the walls of the combustion chamber. The direction of swirl is such that air travels from the fuel injection nozzle toward the spark plug.
As noted herein a cavity formed in the piston tends to promote swirling of incoming air. More specifically, air is aspirated into the engine combustion chamber and caused to initially swirl by virtue of the intake valve and port shape. Thereafter, on the compression stroke, the rate of swirl is increased as the air is compressed into the combustion chamber and the small diameter piston cavity.
Although the concept of a cavity formed within a piston face has been utilized in several forms and variations to achieve varying purposes, the desired uniform charge forming criteria has not been fully attained. For example, the cavity configuration within a piston has been shown by the prior art in the form of a simple cup-like arrangement wherein the latter is provided with cylindrical walls opening at the piston face. Also, the use of a substantially spherical cavity which opens onto the piston face is known. In either instance the primary purpose of these depressed cup formations has been to form either a preliminary combustion chamber, or the means for promoting the rapid swirl of air through the cup and through the cylindrical combustion chamber.
A primary object of the present invention then is to provide an internal combustion engine piston construction having a piston face capable of promoting a more rapid, controlled combustion of a charge.
A further object is to provide a piston having a cavity or depression formed therein and terminating at the piston face, which cavity will receive a stream of fuel as well as swirling air, whereby to force an efficient mixing of the two into a combustible charge.
Still another object is to provide a piston having a cavity formed in the face thereof, as well as one or more supplementary depressions which receive air and burning fuel-air mixture which is spilled from the cavity during a power stroke whereby to assure more uniform and rapid combustion of the engine charge.
The above noted objectives are achieved, and the desired efficient operation of an internal combustion engine is obtained in the present invention by providing means for introducing a swirling air charge to the engine's one or more cylinders on the intake stroke of each. Each piston is provided with a cavity having a central axis extending substantially parallel to the piston axis and opening at the piston face.
Each piston is further provided with at least one and preferably with a plurality of depressions. The latter are formed into the piston face, being spaced and arranged to receive air which is drawn from the main cavity and into the cylinder combustion chamber during the power stroke. The overall effect is that the resulting turbulence induced by the air flowing through and across the various supplementary depressions, serves to more completely mix the charge and consequently promote a uniform combustion event.